The invention relates to a photochromic article formed by applying a novel stabilizing polymeric matrix on a transparent substrate, which matrix includes a photochromic dye and an agent that stabilizes the dye against light being grafted onto the matrix.
Organic photochromic materials are well known. They comprise a polymer matrix including a photochromic dye. One drawback of most of these materials is that their photochromic properties degrade too rapidly so that it is not possible to manufacture commercially usable articles from them, because their lifespan is insufficient. This degradation of the photochromic properties is due to a fatigue of the photochromic dye caused by light. Thus, there has been a need for many years for stable organic photochromic materials.
Several methods have been suggested for producing such a product. For example, it has been suggested to incorporate photochromic dyes into polymerizable compositions in order to impart photochromic properties to the resulting polymer. The difliculty in this approach lies in the fact that the photochromic dyes are sometimes destroyed during the polymerization. Recently, several novel suggestions have been disclosed for alleviating such problems. Examples of such solutions are disclosed in co-pending, co-assigned U.S. provisional patent application Ser. Nos. 60/000,829, 60/001,677, 60/004,492, and 60/011,429.
EP A 0195898 and its equivalent U.S. Pat. No. 4,720,356 describe the incorporation in the composition of the polymerizable matrix of a hindered amine as light stabilizer routinely called HALS. (Hindered, in this sense relates to steric hindrance.) Although the addition of a HALS to the polymerizable matrix composition considerably improves the resistance to fatigue of the photochromic dye, more durable photochromic materials are still needed.
The object of the invention is to satisfy this need.